Anatomical Changes of a Cryogenic Jet in Transition to the Thermodynamic Supercritical Condition.

摘要

The high pressure supercritical facility at the Air Force Research Laboratory at Edwards Air Force Base is used to investigate the effects of chamber pressure (density) ranging from the thermodynamic subcritical to supercritical values at a supercritical chamber temperature. At subcritical pressures, the jets exhibit wave-like structures that amplify downstream and eventually break up into irregularly shaped small entities. The formation of many droplets is seen at higher pressures, resembling a second wind-induced liquid-jet breakup. Further increase of chamber pressure, near the critical condition, fails to induce the transition into a full liquid atomization regime. At this point, the jet anatomy changes abruptly to imitate turbulent gas jet injection. The jet initial growth rate is plotted against the chamber-to- injectant density ratio, along with available data on other liquid/gaseous jets and mixing layers, producing a unique and informative graph. For supercritical conditions, our measured growth rate agrees well with a theoretical equation proposed by Papamoschou and Roshko and closely follows the trend of Dimotakis for incompressible but variable-density gaseous turbulent mixing layers. Fractal analysis of the jet interface also shows a similarity to gas jet behavior with comparable fractal dimension. This is the first time quantitative evidence has been provided to support qualitative visualizations suggesting that supercritical jets appear to behave like conventional gas jets. (6 figures, 21 refs.).